#include<bits/stdc++.h>
using namespace std;
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
const int N = 2e5 + 10;
#define INF 0x3f3f3f3f;
typedef long long int ll;
#define close(); std::ios::sync_with_stdio(false);cin.tie(0),cout.tie(0);
//----------------------------------------------------------------------------//
int n;
void solve()
{
    cin >> n;
    string s;
    cin >> s;

    int pos = 0;
    bool ok = false;
    bool no_change = true;
    for (auto& k : s)
    {
        if (k == '?')
        {
            no_change = false;
            break;
        }
    }
    if (no_change)
    {
        for (int i = 0; i < n; i++) cout << s[i];
        cout << '\n';
        return;
    }
    for (int i = 0; i < n; i++)
    {
        if (s[i] != '?')
        {
            pos = i;
            ok = true;
            break;
        }
    }

    if (ok)
    {
        for (int i = pos; i < n - 1; i++)
        {
            if (s[i + 1] == '?')
            {
                if (s[i] == 'B') s[i + 1] = 'R';
                else s[i + 1] = 'B';
            }
        }

        for (int i = pos; i > 0; i--)
        {
            if (s[i - 1] == '?')
            {
                if (s[i] == 'B') s[i - 1] = 'R';
                else s[i - 1] = 'B';
            }
        }
    }
    else
    {
        for (int i = 0; i < n; i++)
        {
            if (i & 1) s[i] = 'R';
            else s[i] = 'B';
        }
    }

    for (int i = 0; i < n; i++) cout << s[i];
    cout << '\n';






}

int main()
{
    close();
    int T;
    cin >> T;
    while (T--) solve();
    return 0;
}